Your statement sounds like you're joking, but either way, it means someone died. It'll be back to normal after 2 days, assuming the story stays on the front page for 2 days.

EDIT: Seems like it got taken down now.

"Occasionally, there will be a thin black bar at the top of the top bar, in memoriam of a significant figure in the tech/science community dying." -- https://github.com/minimaxir/hacker-news-undocumented#thin-b...

They do this temporarily when someone dies.

Tell me you don’t visit HN often without telling me you don’t visit HN often.